Gene Discovery - Immunotherapy has been most successful when targeted to differentiation antigens expressed on hematopoietic tumors and melanomas in large part because the target antigens are not expressed on essential cells or organs. Other cancers in which this approach could be successful are prostate, breast and ovary. To identify target antigens in prostate and breast cancers we have developed a computer based method to search the EST data base for ESTs that are expressed in prostate or breast cancer and not other essential organs or cells. We have validated this approach experimentally and used it to identify prostate specific members of the MAGE/GAGE family which we term PAGE. We also found evidence for high level expression of a novel T-cell receptor gamma transcript in prostate and breast cancer that encodes a small nuclear protein which resembles a transcriptional regulatory protein.